1. Field of the Invention
The present invention is directed to improved sorption cooling devices and methods for using sorption cooling devices. In particular, the present invention is directed to sorption cooling devices that are particularly adapted to maintain a reduced temperature within an enclosed container for an extended period of time. The cooling devices are particularly useful for temperature-controlled shipping containers that must maintain a temperature below ambient for extended time periods, such as from 1 hour to about 120 hours, or more.
2. Description of Related Art
The shipment of products that must have their temperature maintained within a specific range below ambient is one of the fastest growing market segments in the modern shipping industry. This growth is driven by a number of factors including widespread concerns about safety in the cold food distribution chain, increasing numbers of pharmaceutical and life sciences products which must have their temperature maintained within certain limits, the rapid growth in high-value specialty chemicals such as those used in the semiconductor industry, the increasing number of sophisticated medical tests which require the shipment of patient specimens to an external laboratory, the increased number of clinical trials associated with new pharmaceutical discovery and the increased delivery of products directly to the customer as a result of Internet ordering.
This field is generally referred to as controlled temperature packaging (CTP). TP can be segmented by the target temperature range, namely: frozen (below 0° C.); 2° to 8° C.; and less than ambient (e.g., less than 30° C). In addition, CTP may be segmented by container size, namely: greater than pallet; one cubic foot to pallet; and less than one cubic foot. Containers having a size greater than pallet are typically cooled by mechanical refrigeration and the shipment times are typically from days to many weeks. The one cubic foot to pallet size segment is dominated by systems using ice (e.g., gel packs) and/or dry ice as a coolant wherein the containers are insulated using expanded polystyrene (EPS). The market segment for containers less than one cubic foot in size is very limited due to an unmet need for a small, lightweight cooling mechanism.
Although many basic ice/EPS systems are in use, there is a wide variation in quality and performance of the packaging depending on the value of the product and the sensitivity of the product to temperature fluctuation. A relatively simple system includes a cardboard box into which EPS sheets have been cut and placed. The container is then filled with dry ice in which, for example, frozen fish is shipped. A more sophisticated approach is a validated system consisting of custom molded EPS forms in a rigid box with both frozen and warm gel packs, the combination of which has been tested through a range of temperature cycles for specified thermal properties. Such a validated system can be used for shipping pharmaceuticals. For example, many pharmaceutical products such as vaccines and antibodies must be maintained within a range of 2° C. to 8° C.
The existing ice/EPS cooling system is unsatisfactory for various reasons including: increased environmental concerns associated with the disposal of large quantities of EPS and gel packs; the high cost of shipping; and the required freezers at the shipping source to maintain the frozen packs. The high cost of shipping is directly related to the high volume associated with the EPS and the high volume and mass associated with the gel packs. For a one cubic foot box with a 60 hour lifetime at 2° C. to 8° C., over 90 percent of the volume is consumed by EPS and gel packs. Some reduction in volume and shipping costs may be obtained by using vacuum insulation panels (VIPs), but the high cost of VIPs has precluded significant market penetration.
An example of the foregoing system is illustrated in U.S. Pat. No. 5,924,302 by Derifield issued on Jul. 20, 1999. This patent illustrates a shipping container that includes a plurality of cavities adapted to receive a coolant (e.g., gel packs) that surround a cavity adapted to receive an item to be shipped.
Electrically cooled shipping containers are illustrated in U.S. Pat. No. 6,192,703 by Salyer et al., issued on Feb. 27, 2001. This patent discloses a portable refrigerator unit and storage container employing vacuum insulation panels and a phase change material. Phase change materials undergo a change in physical form (e.g., solid to liquid) thereby absorbing heat from the surrounding environment. A battery driven refrigeration system provides cooling of the shipping container.
The use of reactor-based rechargeable portable coolers are illustrated in U.S. Pat. No. 5,186,020 by Rockenfeller et al., issued on Feb. 16, 1993. This patent discloses a portable cooler utilizing a gas-liquid-gas phase change to effect cooling of chamber. However, the reactor-based apparatus disclosed by Rockenfeller et al. requires a source of electricity to effect the initial gas-liquid phase change. As a result, the apparatus occupies additional space and has additional weight, making it cost-ineffective and severely impairing its utility either for a single-use basis or for a shipping container.
A sorption cooler is illustrated in U.S. Pat. No. 5,048,301 by Sabin et al. This patent discloses a sorption cooling unit where the cooling liquid is maintained in the evaporator prior to the sorption process. A disadvantage of this device is that too much energy is consumed by having to cool the cooling liquid in the evaporator upon activation of the sorption unit. Space is also wasted in that the evaporator will require a relatively large volume to enable an efficient evaporation process because both the liquid and evaporation volume are located in the same general space. Furthermore, space limitations restrict the amount of cooling liquid that may be maintained in the evaporator.
Thus, there is a need for a temperature-controlled container, such as a shipping container, having a lightweight cooling device that does not occupy a large volume. It would also be advantageous if the temperature of the container was controllable over a range of temperatures. It would also be advantageous if the cooling device had the ability to maintain the reduced temperature for an extended period of time. It would also be advantageous if the cooling device could be used cost effectively on a single-use basis.